Final answer:
Ozone forms naturally in the upper atmosphere and acts as a barrier to harmful UV radiation from the sun.
Step-by-step explanation:
Ozone forms naturally in the upper atmosphere by the action of ultraviolet light from the sun on the oxygen there. Most atmospheric ozone occurs in the stratosphere, a layer of the atmosphere extending from about 10 to 50 kilometers above the earth's surface. This ozone acts as a barrier to harmful ultraviolet light from the sun by absorbing it via a chemical decomposition reaction: ultraviolet light